1. Field of the Invention
The present invention relates to stage lighting and particularly to a compact follow spotlight for stage lighting applications.
2. Description of the Prior Art
A follow spot is used to achieve the special stage lighting effect wherein an actor is illuminated by a circle of light which follows him as he moves about the stage. In a conventional follow spot, a high intensity lamp with a rear reflector is projected through a pattern matte and/or an iris and through a lens that focuses a distant image of the pattern or iris on the stage. Iris adjustment permits variation of the iris image size. The spot housing is mounted to pivot both horizontally and vertically, thereby permitting the operator to move the spotlight so as to follow the actor.
Certain shortcomings are characteristics of prior art follow spots. First, the optical arrangement necessitates a relatively long housing. For example, a typical follow spot having a 75 foot throw has a housing almost 31/2 feet long. Installation in small quarters is impossible. A principal object of the present invention is to provide a compact follow spot which is significantly shorter, typically one-half the length of the prior art devices.
Another shortcoming of known follow spots relates to heat entrapment. When a conventional follow spot is tilted downwardly toward the stage, some heat from the lamp is trapped between the lamp and its reflector. The resultant temperature increase may shorten the lamp lifetime. Another object of the present invention is to provide a follow spot in which such heat entrapment does not occur, and in which natural draft venting takes place with downward tilting of the housing.
A further problem is that the refracting lenses in prior art devices may introduce both light loss and chromatic aberration. An object of this invention is to provide a follow spot that is achromatic and substantially free of light loss.
One prior art attempt to overcome these shortcomings placed the light source behind a spherical or parabolic main mirror having a central hole. Light projects forwardly through the hole, is reflected back to the main mirror by a convex mirror in front, and finally is reflected toward the stage by the parabolic mirror. Such an arrangement is shown, e.g., in the U.S. Pat. No. 2,755,374 to Ott and Oberholzer. Reflective optics minimize light loss and are achromatic, but the amount of light projected is limited by the central hole size, and the coaxial alignment of mirrors and light source does not minimize the light loss.
An off-axis reflective organization for use in an automobile headlight is suggested by the British patent No. 399,121 (1933). This device utilizes a paraboloid reflector which produces an unfocused light beam of diverging shape when illuminated by an off-axis source lamp. The beam includes both parallel rays produced by reflection of light from the lamp that passes through the focus of the paraboloid, and offset or diverging rays resultant from light situated slightly outside the focus. Such an unfocused beam is totally unsatisfactory for follow spot theatrical lighting applications.